OPENDJ-1886: Remove short option for testonly arg

*****  opendj-cli *****
* ArgumentConstants.java
** Add constant for testonly long option

* CommonArguments.java
** Removes getTestOnly(...) static method as it is only used in InstallDS.

* cli.properties
** Removes INFO_ARGUMENT_DESCRIPTION_TESTONLY message and migrate it to server tool.properties to have consistant import in InstallDS.java

***** opendj-ldap-toolkit *****
* resources/.../_script_util.bat
** Replace short option call by long option call

***** opendj-server-legacy *****
* resources/.../bin/_script-util.sh _script-util.bat
** Replace short option call by long option call

* InstallDSArgumentParser.java
** Inline static call to CommonArguments

* tools.properties
** Add testonly argument information message